The present invention relates to a device for measuring vibration which is particularly useful for monitoring the operation of electrical equipment, although its usefulness is obviously not limited to this particular application.
In many instances, it is desirable to measure vibration, and transmit that measurement to a remote location. In electrical equipment such as large generators, for example, it is desirable to monitor the machine to detect the occurrence of abnormal vibration in the stator windings, the stator core, or other parts of the machine. Fiber optics provide a very desirable means for transmitting this information since a light guide consist of glass fibers, which are insulating and not affected by high voltages, magnetic fields, high temperature, or other environmental influences to which they may be subjected. Various devices have been employed for the measurement of vibration, incorporating light guides to transmit light between a light source and a receiver, crossing the path of a vibratory vane. Frequently the intensity of light transmitted by the receiving light guide is determined, and, by converting it to an electrical signal, it can be conveniently used to indicate the amplitude of movement of the vane. Such a system, however, has serious limitations. For example, such a system can only be employed to measure amplitudes which are comparable to the diameter of the light guide. A more serious deficiency of such a system is that any change in intensity of the light source from which the light signal is obtained, or in the sensitivity of the electrical detection means, or in the optical transmission characteristics of the light guides, results in a change in the amount of observed light and thus causes an erroneous measurement.